Efficacy and pharmacokinetics of febantel and ivermectin in red deer (Cervus elaphus)

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Abstract
A trial was conducted to determine the efficacy and pharmacokinetics of febantel and ivermectin in six-month-old red deer calves (C elaphus). Five calves received febantel by mouth at 7.5 mg/kg, five received a subcutaneous injection of ivermectin at 200 ug/kg and five were controls. All calves were killed seven days later and total lung and gastrointestinal worm counts carried out. Febantel was 85 and 99.8% efficient in removing immature and mature Dictyocaulus viviparus, respectively, and ivermectin was 100% efficient in both cases. There was no gastro-intestinal nematodes in any of the treated calves, compared to an average of 619 in the control calves. The metabolism of febantel resulted in plasma levels of fenbendazole, oxfendazole and sulphone for which the common curves fitted by compartmental model peaked at values (standard errors) of 0.46 (0.03), 0.41 (0.02) and 1.73 (0.07) mg/1 after approximately five, nine, and thirteen hours and were undetectable at 30, 72 and 120 hours respectively. There was considerable variation among animals in response to ivermectin. The fitted common curve had a peak plasma level of 15.8 (0.08) ug/1 at 20 hours after injection, which had dropped to 7.9 (1.1) ug/1 seven days after injection. It was estimated that after 15 days plasma levels of ivermectin would not be detectable. It is concluded that the injectable form of ivermectin tested is a highly efficient anthelmintic in deer, and that plasma levels persist for over a week after subcutaneous injection. Febantel is very efficient against mature D. viviparus in deer, but its reduced efficiency against immature D. viviparus may relate to the deer's ability to metabolise and excrete benzimidazoles more quickly than sheep and cattle.